Fix SSH privatekey in basic_26

Change-Id: Iee0a30314d90288121364e2ea385d2b1fdd8df2a
Signed-off-by: Gabriel Cuba <gcuba@whitestack.com>

robot-systest/testsuite/basic_26-secure_helm_execution_environment.robot

@@ -42,7 +42,7 @@ ${ns_timeout}   5min
 ${username}   ubuntu
 ${password}   ${EMPTY}
 ${publickey}   %{HOME}/.ssh/id_rsa.pub
-${privatekey}   %{OSM_RSA_FILE}
+${privatekey}   %{HOME}/.ssh/id_rsa
 
 # SSH keys and username to be used to connect to OSM VM
 ${osm_host}   %{OSM_HOSTNAME}